In general, radical polymerizable resins typified by unsaturated polyester resins, vinyl ester resins, urethane (meth)acrylic resins, polyester (meth)acrylate resins, (meth)acrylate resins, etc., are materials that provide cured products excellent in mechanical strength, water resistance, etc. As such radical polymerizable resins have a curing time period that can be adjusted without being influenced by atmospheric temperature by adjusting a curing agent or an accelerator. Therefore, unlike epoxy resins, curing thereof does not take a long period of time and poor curing does not occur when the resins are treated especially at low temperatures. For this reason, the radical polymerizable resins have been conventionally widely used in coating materials, adhesives, fiber reinforced plastic molding materials, etc.
Among the radical polymerizable resins, vinyl ester resins provide cured products with excellent acid and alkali resistance, and cold curing properties. Hence they are widely used for various applications, for example, FRP molded articles such as corrosion resistant tanks and corrosion-proof FRP linings. Moreover, cured products obtained from the vinyl ester resins are transparent. Therefore, when the cured products are used for containers such as tanks, there is the merit that the remaining amount of liquid or the like in the container can be easily confirmed.
However, since containers such as tanks manufactured using the vinyl ester resins do not have enough toughness (impact resistance) to be able to withstand pressures such as internal or external pressures and impact from the outside, there is a problem in that cracking due to pressure or impact occurs.
On the other hand, in order to increase the impact resistance of the cured products, various studies have been made. For example, a resin composition containing an epoxy vinyl ester resin, a urethane vinyl ester resin, and a coreactive monomer such as styrene is known (e.g., see Patent Document 1). In such a resin composition as described above, the impact resistance is improved using a second phase in which the urethane vinyl ester resin is formed by dispersion (i.e., microphase separated) in the epoxy vinyl ester resin at the time of curing.
However, such a resin composition as described above has a problem in that a transparent cured product cannot be obtained because of the turbidity resulting from microphase separation, which occurs at the time of curing.
Further, methacrylic resins obtained by copolymerization of methyl methacrylate and a specific compound (e.g., see Patent Document 2), and resin compositions containing an acid modified epoxy acrylate which is obtained by adding polybasic acid anhydride to a part or a whole of a hydroxy group present in epoxy acrylate, a thermoplastic polymer, a compound having two or more double bonds in one molecule, and a reactive monomer having a single double bond in one molecule (e.g., see Patent Document 3) are also known.
Molding materials which contain such resins and such resin compositions can provide transparent cured products excellent in impact resistance, however they have problems in that the cured products have insufficient corrosion resistance, and thus cannot be used for containers such as tanks which require corrosion resistance.
As described above, molding materials containing the conventional resins or resin compositions do not successfully provide cured products with excellent impact resistance, corrosion resistance and transparency.
Patent Document 1: JP 2001-500177 A
Patent Document 2: JP 2003-128729 A
Patent Document 3: JP 2002-138121 A